Many devices obtain their electrical operating power from a source with irregular availability, but must be able to operate even when the source is providing no power or insufficient power. Similarly, some devices occasionally require a short burst of increased electrical power that their normal power source is unable to supply. Although rechargeable batteries with a battery charger can be used for some of these applications, batteries are unfeasible for many other applications, due to cost, size, weight, or other considerations. Passive radio frequency identification (RFID) tags are one example of such devices. They get their operating power by harvesting a portion of the energy received through their antenna from a nearby transmitting wireless device, and the harvested energy is sufficient to operate the tag's circuit. The RFID tag works well when the incoming signal is strong, but may be unreliable when the incoming signal is weak or erratic, and the tag stops completely when the incoming signal stops and thereby denies the tag its source of power. Temporarily storing excess energy for use when it's needed would be very beneficial, but batteries are impractical for use in most RFID tags, and the circuitry may be much too small to contain a storage capacitor of the required size.